Moisture sensitive element and method of preparing the same



June 2, 1964 FENNER 3,135,117

I MOISTURE SENSITIVE ELEMENT AND METHOD OF PREPARING THE'SAME Filed June 1, 1960 2 Sheets-Sheet l Fig. 2c

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PARTIAL VAPOR PRESSURE (mcues OF MERCURY) mmvroa Ralph L. Fenner "635M @@Z Q Attorneys United States Patent 3,135,117 MOISTURE SENSITIVE ELEMENT AND METHOD OF PREPARING THE SAME Ralph L. Fennel, 45 Harrison Ave., Sausalito, Calif. Filed June 1, 1960, Ser. No. 33,288 7 Claims. (Q1. 73-637) This invention relates to a moisture sensitive element and method of preparing the same.

Conventional moisture measuring devices have been of very low accuracy particularly when it is desired to meas ure a very low moisture content or a very high moisture content. This has been true because no particularly satisfactory moisture sensing element or means has been available. There is, therefore, a great need for a moisture sensitive element which is accurate when measuring all ranges of moisture content.

In general, it is an object of the present invention to provide a moisture sensitive element which is responsive to moisture conditions rangingfrom a dry state to a saturated state.

Another object of the invention is to provide a moisture sensing element of the above character which is accurate through moisture levels approaching Zero relative humidity in the vapor phase and moisture levels associated with 100 percent relative humidity in the vapor phase.

Another object of the invention is to provide a moisture sensitive element of the above character which has a large response for small changes in moisture content or level.

Another object of the invention is to provide a moisture sensitive element of the above character which is sensitive at extremely high and low temperatures.

Another object of the invention is to provide a moisture sensitive element of the above character which will respond accurately for long periods of time without recalibration.

Another object of the invention is to provide a moisture sensitive element of the above character which can measure moisture content in gases and liquids.

Another object of the invention is to provide a moisture sensitive element of the above character which can be immersed in water and other solvents without destroying its ability to respond to moisture content.

Another object of the invention is to provide a moisture sensing element of the above character which can sense the proportion of liquid water in a mixture or solution containing water and non-polar liquids.

Another object of the invention is to provide a moisture sensing element of the above character which will give an accurate measure of relative humidity under rapidly changing vapor pressures.

Another object of the invention is to provide a moisture sensing element of the above character which will give an accurate response to the equilibrium moisture content in Wood fiber under adsorb and desorb moisture conditions.

Another object of the invention is to provide a moisture sensing element of the above character which can withstand shock and vibration.

Another object of the invention is to provide a moisture sensing element of the above character which has an output force which is suificient to directly drive indicating mechanisms.

Another object of the invention is to provide a method for preparing the moisture sensitive element.

Another object of the invention is to provide a method for preparing the tail-like appendage of the seed from the genus Erodiuni to provide a moisture sensitive element.

Another object of the invention is to provide a moisture sensitive element of the above character which can be made more sensitive to a predetermined moisture content range.

3,135,117 Patented June 2, 1964 Additional objects and features of the invention will appear from the following description in which the preferred embodiments and methods have been set forth in detail in conjunction with the accompanying drawings.

Referring to the drawings:

FIGURE 1A shows a moisture sensitive element in the form of a seed of the genus Erodium and in a dry state.

FIGURE 1B shows the same moisture sensitive element in a Wet or saturated state.

FIGURE 2A shows the tail-like appendage of the seed of the genus Erodium and in the condition when it is measuring zero percent relative humidity.

FIGURE 2B shows the same moisture sensitive element in FIGURE 2A measuring percent relative humidity.

FIGURE 2C shows the same moisture sensitive element in FIGURE 2B measuring percent relative humidity.

FIGURE 3 is a graph showing the sensitivity of the moisture sensitive element.

FIGURE 4 is a graph showing sensitivity of the moisture sensitive element for absorb and desorb cycles.

FIGURE 5 is a graph showing the relationship between relative humidity, temperature, partial vapor pressure and relative moisture content.

In general, my invention consists of a moisture sensitive element which is capable of sensing relative moisture content. It is comprised of a member having two superposed layers one of which is relatively sensitive to moisture, and the other of which is relatively insensitive to moisture; or in other words, one of which absorbs moisture and the other of which is relatively impervious to moisture. Changes in moisture content in the moisture absorbing layer cause deformation of the member and give an indication of the moisture content in the moisture absorbing layer.

Certain members have been found to be particularly adapted for use as moisture sensing elements. In particular, I have found that the tail-like appendages of the seeds of the genus Erodium have characteristics which particularly adapt them for use as moisture sensitive elements. The genus Erodiurn commonly called Storks Bill, Alfilarilla, or Filaree, is an annual herb which is characterized by pinately veined and lobed lead blades,

five sepals, five petals and five stamens alternating with five scale-like staminodia. The seeds of this genus have tail-like appendages with elongate columns. The taillike appendages are bearded inside and are spirally coiled when freed from the central axis. The species texanum, macrophyllum, cygnorum, botrys, moschutum and cicutarium yield tail-like appendages having a length and other characteristics which particularly adapt them for use as moisture sensitive elements. This is particularly true of the species botrys which has a length of 5 to 8 centimeters and which is practically straight when wet and has approximately 16 turns when dry.

In FIGURE 1A a seed in a dry condition of the species botrys is shown, whereas in FIGURE 1B the same seed is shown in a wet or saturated condition. The seed 11 consists of a basal ovary 12, an intermediate columnar taillike appendage 13, and a terminal or tail portion 14. When viewed under a microscope, it is found that the style is comprised of two superposed contiguous layers, one of which readily absorbs moisture and the other of which is relatively impervious to moisture. The layer which readily absorbs moisture appears to be comprised of translucent extremely long cells, whereas the layer which is relatively impervious to moisture appears to be comprised of relatively short cells. The two fiber-like layers are covered with a coating 16 which has hair-like structures 17 called beards protruding therefrom.

In observing the seeds of the genus Erodium, I have found that the function of the tail-like appendage of the seed is to plant the seeds at a reasonable depth in the soil, as for example, at a depth of of an inch. This burying of the seed or ovary 12 is accomplished by the winding and unwinding of the tail-like appendage 13 in response to changing moisture conditions. When the taillike appendage is dry, it is in the form of a helix and when it becomes moist, it expands and unwinds to drive the sharp pointed seed 12 down into the soil. After the seed is planted deep in the soil, a dehiscent layer between the ovary or seed and the tail-like appendage permits the tail-like appendage to be broken off from the seed and to permit the seed to remain in the ground.

In observing these actions of seeds of this genus, I have found that the twisting and untwisting of the taillike appendage is proportional to the amount of moisture absorbed by the tail-like appendage. By actually weighing the seeds, I was able to determine that there was a direct relationship between the moisture content of the tail-like appendage and the number of turns or twists in the tail-like appendage itself. However, I have observed in the seeds natural state that there is not a good correlation between the moisture content in the tail-like appendage and the radial displacement of the tail-like appendage.

To obtain a good correlation between the moisture content of the tail-like appendage and the number of turns or twists in the tail-like appendage, I have found that the seeds should be prepared in the following manner.

Seeds of a suitable type are collected after they have ripened. After the seeds are collected, they are retted by placing them in a water bath having a temperature over 72 F. and preferably 80 to 100 F. The seeds are allowed to ret or soak in the water for a period of approximately one week to permit bacteria to attack the woody fiber coating 16 and the beards 17 on the tail-like appendage. The two layers of the tail-like appendage have been found to be very resistant to bacterial action and will rot away as will the surface coating 16. If it is desired to speed up the action, the seeds may be boiled in water for 6 or 8 hours which Will also release the skin or coating of the seed.

After the seeds have been allowed to ret for a sufficient period of time, the coating 16 and the beards 1'7 are stripped from the tail-like appendage which is relatively straight because of the saturated condition of the tail-like appendage. The stripping can be accomplished in a suitable manner such as by grasping one of the seeds in one hand and using the fingernails of the other to scrape the outer coating and beards from the tail-like appendage. This is easily accomplished when the seeds have retted for a suflicient period of time. It is possible to determine when the seeds are ready for stripping by merely examining the color of the seeds. When the seeds are first placed in the water, they have a relatively light brown color, whereas when the tail-like appendages are ready to be stripped, the seeds have a relatively dark brown color. Removing the seed capsule and stripping the coating and beards from the tail-like appendage exposes the inner fiber-like structure of the tail-like appendage which has a relatively smooth, hard looking appearance such as shown in FIGURES 2A, 2B and 2C, and which has a relatively dark brown color.

In FIGURE 2A, the tail-like appendage is relatively tightly coiled, particularly at its base end and indicates zero percent relative humidity. In FIGURE 2B, the tail-like appendage has unwound so that it has approximately 3 or 4 turns and indicates a relative humidity of approximately 95 percent. In FIGURE 2C, the taillike appendage is practically straight and indicates a Wet or saturated condition.

When the tail-like appendage of the genus Erodium is properly prepared as hereinbefore explained, the moisture content in the tail-like appendage is proportional to the displacement of the tail-like appendage. As shown in FIGURE 3, in plotting the relative number of turns in the tail-like appendage in percent against the relative moisture content in percent, a practically straight line relationship is formed. This is important because this indicates that the tail-like appendage retains its sensitivity at-the zero and 100 percent regions of moisture content. However, the curve in FIGURE 3 actually shows a greater sensitivity at moisture contents approaching 100 percent and actually as can be seen, the curve almost becomes asymptotic when measuring a high moisture content. By relative moisture content, I mean the relative amount of moisture that a fiber can hold at a given temperature, relative humidity and vapor pressure as opposed to the amount of moisture that the fiber can hold at saturation. Thus, when the moisture sensitive element is dry and coiled, it would give a reading of zero percent relative moisture content, whereas at saturation when the moisture sensitive element is relatively straight, 60 to percent of the element would be water and this condition would correspond to percent relative moisture content.

The moisture content in the tail-like appendage is determined by the moisture content of the surrounding atmosphere and increases or decreases as the moisture in the surrounding atmosphere increases or decreases. This is illustrated in the absorb and desorb curves shown in FIGURE 4. The absorb curve is formed when the relative humidity is increasing and the desorb curve is formed when the relative humidity is decreasing. The moisture sensitive element, however, does not actually measure relative humidity. It actually measures the moisture content as a wood fiber exposed to the surrounding air. In order to make an exact determination of the moisture content in the air, it is necessary to know whether the moisture content in the air is increasing or decreasing so that it can be determined whether the desorb or absorb curves should be utilized.

It will be appreciated that the curve in FIGURE 4 does not go into the water-filled state because only relative humidity is being measured by the moisture sensitive element. The moisture sensitive element measures the amount of moisture in the air in comparison to the amount of moisture the air can hold at a predetermined temperature. Thus, when the moisture sensitive element is sensing near 100 percent relative humidity as, for example, at 23 C. as shown in FIGURE 4, the moisture sensitive element still is not completely uncoiled because the relative moisture content of the moisture sensitive element is much less than the percent of relative humidity.

As iswell known to those skilled in the art, there is a relationship between the moisture content of fibers, vapor pressure and temperature. The chart shown in FIGURE 5 sets forth this relationship. In the chart in FIGURE 5, the moisture content is given in relative number of turns in percent of the moisture sensitive element. Heretofore, such charts have been utilized to determine the moisture content of organic fibers by determining the vapor pressure, the relative humidity and temperature, and then reading the moisture content from the chart. However, when used in this manner, such charts have not given accurate results because the charts are based on oscillating vapor pressures which are normally not found in the environment in which organic fibers are present. Errors as great as 4 to 5 percent can be made in determining moisture content with such charts. Oscillating vapor pressures are used in making such charts because of the difference between the absorb and desorb cycles of organic fibers. For the same reason, it is necessary to known whether the relative humidity is increasing or decreasing before an accurate determination of moisture content can be made.

Use of my moisture sensitive element makes it possible to determine the moisture contentdirectly without reference to the chart. Since the moisture content can be determined directly, other variables can be determined with a chart such as that shown in FIGURE 5. For example, if the relative number of turns of the moisture sensitive element is known and two of the other variables in the chart in FIGURE 5 are known, the other variable can be readily ascertained.

When determining the relative moisture content of a wood iiber with my moisture sensitive element, a reading of the condition of the moisture sensitive element would be made after it has had an opportunity to measure the moisture content of the wood fiber. When the moisture sensitive element is 50 percent saturated, this would indicate that the wood fiber of which an analysis is being made is also 50 percent saturated. Thus, if this wood fiber of which an analysis is being made is Ponerosa pine which is approximately 32 percent moisture at saturation, then the Ponderosa pine being examined would be 16 percent moisture by weight. If the moisture sensitive element reads 100 percent, then the Ponderosa pine would be 32 percent water by weight.

Thus, in general, the moisture sensitive element measures the relative amount of moisture in the surrounding materials. For example, when placed in a room, the moisture sensitive element would measure the relative amount of moisture in the surrounding fibers, clothing, draperies, paper and the like.

In certain applications as described in my copending application Serial No. 33,319, filed June 1, 1960, I have found it desirable to make the tail-like appendage or moisture sensitive element more sensitive to moisture changes. This has been found to be necessary because when the tail-like appendage is in a dry state, the tail-like appendage is tightly wound into a helix so that the layer sensitive to moisture is compietely enclosed within the outer relatively impervious layer. This makes it diflicult for air to come into contact with the inner sensitive layer of the tail-like appendage. Because of this fact, when the taillike appendage is in a dry state, there is a time delay in sensing a moisture change until the tail-like appendage has unwound sutficiently so that it is possible for air to pass freely between the turns of the tail-like appendage.

When examining the tail-like appendage of the genus Erodium, I have found that there is a weak layer dividing the tail-like appendage into two equal longitudinal parts. When the tail-like appendage is in a wet state, by the use of dissecting needles or other suitable means, the tail-like appendage can be split into two equal parts. After the tail-like appendage has been split into two equal parts, the two parts are allowed to dry and re-curl separately. With the tail-like appendage split apart, the two separate parts when they are completely dry still have spaces between the turns which form the helix so that it is very easy for air to pass through between the turns and to come into intimate contact with the inner moisture sensitive layer of the tail-like appendage.

This is particularly important for restrained operation of the moisture sensitive element as described in my copending application Serial No. 33,319, filed June 1, 1960.

Splitting of the tail-like appendage in this manner does not affect the sensitivity or accuracy of the tail-like appendage. The separated parts still generate sufficient torque during the absorb and desorb cycles to directly drive indicating instruments as described in my copending application Serial No. 33,319, filed June 1, 1960.

It is also possible to make my moisture sensitive ele- 'rnent more sensitive to changes in moisture content. This is accomplished by coating the moisture sensitive element with a suitable deliquescent material such as lithium or completely unwound condition at 20 or 30 percent relative humidity. In this way, the moisture sensitive element will change from a completely uncoiled state to a completely coiled state in a relative humidity changing from Zero to 20 or 30 percent. The upper limit of the relative humidity which can be measured is determined by the tinckness of the coating of the lithium chloride on the moisture sensitive element. Where it is desired to measure higher relative humidities, a thinner coating of lithium chloride is applied to the moisture sensitive element.

Lithium cifloride can be applied to the moisture sensitive element in any suitable manner such as dipping the moisture sensitive element in a lithium chloride and water ties are experienced, the moisture sensitive element can be coated with lithium chloride so that it is in a saturated solution.

It is apparent from the foregoing that I have provided a moisture sensitive element which is responsive to moisture conditions ranging from a dry state to a saturated state and that the moisture sensitive element can be made more sensitive for relatively small ranges of relative humidity. The moisture sensitive element can be produced readily and when properly calibrated will retain its calibration for long periods of time. It can be utilized for measuring the moisture content in gases and the amount of moisture in liquids. The moisture sensitive element is constructed of such a material that it is not destroyed by solvents.

I claim:

1. In a method for preparing a moisture sensitive element from the seed of the genus Erodium the seed being characterized in that it has a seed capsule with a tail-like appendage attached thereto, the tail-like appendage being a relatively hard fibrous structure covered with an outer coating having beards thereon, retting the seed, removing the seed capsule, and stripping the outer coating and beards of the tail-like appendage to expose the relatively hard fibrous structure of the tail-like appendage.

2. A method as in claim 1 wherein the retting of the seed is carried on for a sufiicient period of time to allow the bacteria to attack the outer covering of the tail-like appendage so that the outer covering can be readily removed.

3. A method as in claim 1 together with the step of splitting the tail-like appendage longitudinally to provide at least two parts.

4. A method as in claim 1 together with the step of coating the tail-like appendage with a deliquescent material after the outer coating has been removed.

5. A moisture sensitive element comprised of the taillike appendage of the seed of the genus Erodium, the tail-like appendage being characterized in that it has an outer covering which covers the moisture absorbing cells in the tail-like appendage, said outer covering being stripped away from the tail-like appendage to expose the moisture absorbing cells to the atmosphere.

6. A moisture sensitive element as in claim 5 wherein the tail-like appendage has been split longitudinally to provide at least two separate parts.

7. A moisture sensitive element as in claim 5 coated with a deliquescent material.

References Cited in the file of this patent UNITED STATES PATENTS 51,477 Rand Dec. 12, 1865 182,779 Wagner Oct. 3, 1876 183,062 Meucci Oct. 10, 1876 1,675,302 Roemer June 26, 1928 2,504,299 Cartwright Apr. 18, 1950 FOREIGN PATENTS 5,235 Great Britain Apr. 9, 1887 

5. A MOISTURE SENSITIVE ELEMENT COMPRISED OF THE TAILLIKE APPENDAGE OF THE SEED OF THE GENUS ERODIUM, THE TAIL-LIKE APPENDAGE BEING CHARACTERIZED IN THAT IT HAS AN OUTER COVERING WHICH COVERS THE MOISTURTE ABSORBING CELLS IN THE TAIL-LIKE APPENDAGE, SAID OUTER COVERING BEING STRIPPED AWAY FROM THE TAIL-LIKE APPENDAGE TO EXPOSE THE MOISTURE ABSORBING CELLS TO THE ATMOSPHERE.
 6. A MOISTURE SENSITIVE ELEMENT AS IN CLAIM 5 WHEREIN THE TAIL-LIKE APPENDAGE HAS BEEN SPLIT LONGITUDINALLY TO PROVIDE AT LEAST TWO SEPARATE PARTS. 